Atmospheric Sciences & Global Change Research Highlights

August 2009

Northern Exposure

Most aerosols in the Arctic region "hitchhiked" there from other places in the world.

A helicopter carries an instrument to the research site in Sweden to obtain new measurements of aerosol particles that affect climate change. At 200 km north of the Arctic Circle, the site is accessible only by foot or helicopter. The meteorology station in the foreground was used for weather data. Enlarge Image

Results: In companion papers published in the Journal of Geophysical Research, a team of U.S., Swiss, and Swedish scientists is revealing new insights about tiny atmospheric particles in the Arctic region, where temperatures are increasing at twice the rate of the rest of the world.

Their most striking discovery: Most of the aerosol particles were likely transported to the Arctic from other places around the world. The research team concluded that the size, number, and chemical composition of Arctic aerosols were similar to those found about a mile high in the mid-latitude troposphere.

Why it matters: The Arctic region represents one of the major uncertainties in the current understanding of climate change, because of its complex interaction of aerosols, clouds, and climate. Until this study, there were few single-particle data on aerosol in the Arctic. This is because of the difficulty in accessing the Arctic and Antarctic regions and the scarcity of organized field missions at high northern and southern latitudes. This study has increased the understanding of the properties of Arctic aerosol and atmospheric chemistry in the Arctic and, as a result, will help reduce the uncertain nature of climate change in the region.

Methods: Using sophisticated measurement instruments, the scientists travelled north of the Arctic Circle to compare and contrast the properties of aerosol particles—tiny bits of dust, soot, and other material in the atmosphere. They found that the composition of the aerosol changed with the origin of the air mass, which is a large body of air that has similar temperature and moisture properties. For example, calcium-rich aerosol particles were most prominent in southern air flow and iron-rich particles dominated the northeastern air flow. The western air flow contained the least amount of mineral particles, which may be similar to the background level in the Arctic and much like that found in the mid latitudes, such as the United States.

The team operated an instrument known the aerosol time-of-flight mass spectrometer at the Abisko Scientific Research Station Stordalen site, administered by the Royal Swedish Academy of Sciences, in northern Sweden. The spectrometer was operated for long periods of time in 2007 from air masses coming from the south, northeast, and west, each having different particle characteristics. Periodically, it was connected to an instrument known as a hygroscopicity tandem differential mobility analyzer to measure aerosol chemical composition as a function of hygroscopic growth. Using this analyzer, the researchers found that sea salt aerosols had the highest hygroscopic growth, meaning the amount of water a particle takes up, and particles from biomass combustion, such as burning wood for domestic heating, had the lowest hygroscopic growth. The more water a particle takes up, the larger it grows, affecting its chemistry and potential to form clouds. The scientists also used a scanning mobility particle sizer, to determine the number and distribution of smaller particles; a condensation particle counter, to determine total number of particles; and a cloud condensation nuclei counter, to determine the number of cloud forming particles. The wind speed, wind direction, and temperature were monitored and back trajectories were determined to differentiate and characterize the air masses.

According to the team, this was the first time that an aerosol time-of-flight mass spectrometer was used at Arctic latitudes. The instrument determines the size, chemical composition, and mixing state of individual particles both in situ and in real time. Those properties play significant roles in atmospheric chemistry, visibility, and climate.

What's next: Data from this study are available for incorporating into climate models. Future studies may be conducted during the winter to look at the yearly variability in the Arctic. This is a unique location where there is complete daylight in summer and darkness in the winter, and it is not known how this affects the particles.

Acknowledgments: PNNL is transforming the nation's ability to transform climate change and its impacts. This work was supported by PNNL's Aerosol Climate Initiative with Laboratory-Directed Research and Development funds, the University of Washington, ETH internal research funding, the Royal Swedish Academy of Sciences, Carleton College, a European Commission/Marie Curie Excellence grant, and the European Union FP6 infrastructure project known as European Supersites for Atmospheric Aerosol Research.